A conventional ball valve is shown in FIGS. 1-3, which includes: a valve casing 1 defining a liquid passage 4 therein, a solid ball 2 rotatably mounted in the valve casing 1 formed with a through hole 3 having a diameter d of the through hole 3, a lever handle 5 connected on a rotating shaft 9 rotatably mounted in the casing for rotating the ball 2, and a pair of valve seats 7 respectively provided on an upstream port and a downstream port of the casing 1 for sealing an aperture 6 between a valve chamber 8 and the ball 2. The valve seat 7 is made of materials having heat and corrosion resistance and durable for pressure and may be made of elastomers such as Teflon. An adapter 10 is provided on each side of the valve casing communicating with the valve chamber 8 to be connected with a piping system (not shown). The rotating shaft 5 is formed with a bottom arcuate portion embedded in an arcuate groove 2a recessed in an upper portion of the ball 2 for driving the ball 2.
When opening a conventional ball valve as shown in FIG. 2, a fluid flows in a direction P from a right side passage 4 of the valve towards a left side passage 4 through the through hole 3. When the valve is closed as shown in FIG. 3, the handle 5 is rotated in 90 degrees to allow the ball 2 to seal the seats 7 to close the valve chamber 8 and aperture 6 and also shield the through hole 3, thereby stopping the fluid flow. A sealing zone of the ball 2 will be sealably engageable with the valve seats 7 for stopping a downstream flow of the liquid through the valve.
Such a conventional ball valve includes the solid ball 2 which is made of heavy metal material. For instance, a ball used for making a ball valve of 12 inches may have a weight of 160 kilograms. Therefore, the heavy weight of the ball will limit the production of ball valves with larger sizes, being unable for maximizing the production of larger ball valve for handling higher flow-rate fluids.
For reducing the weight of the ball, it may be made as a hollow ball body. However, when such a hollow ball is subjected to a high pressure stream or a water hammer action caused by suddenly closing the valve, a deformation of the ball shell will be caused. When such a deformation is beyond an elastic limit of the ball shell, a permanent deformation will then occur. If the permanent deformation influences the ball to exceed a distortion of its sphericity to be 2/100.about.5/100, the ball will lose its sealing effect and valve closing function.